DEFINE: unconditioned stimulus
stimulus innately producing a behaviour
DEFINE: neutral stimulus
stimulus producing no conditioned response
Split-GAL4 system
- split Gal4 into activation domain and DNA binding domain
- attach zipper domain to activation domain and another zipper domain to DNA binding domain
- express activation domain + zipper domain under control of enhancer 1
express DNA binding domain + zipper domain under control of enhancer 2 (different enhancer) - gal4 will only bind to UAS and activate transcription of gene in cells where both DNA binding domain and activation domain are expressed
what cells are the mushroom body made up of?
kenyon cells
mushroom body output neurons
receive input from kenyon cells
how would you show that mushroom body output neurons lead to avoidance/approach behaviour using optogenetics?
- use split-GAL4 system to express optogenetic activator in specific mushroom body output neurons (e.g. the neurons coding avoidance behaviour)
- place flies in behaviour chamber with 4 different quadrants
- shine light in half of the chamber. light activates neurons.
- flies avoid the light? —-> mushroom body output neurons code avoidance behaviour
- repeat for a different mushroom body output neuron (e.g. neuron coding approach behaviour)
- flies approach the light? —> mushroom body output neuron codes approach behaviour
how does learning occur in neural circuits?
e.g. reward dopaminergic neuron and avoidance mushroom body output neuron innervate the same compartment in the mushroom body
reward dopamine signalling depresses synapse between kenyon cells and avoidance output neuron - weakens synapse
less avoidance behaviour
reward behaviour unaffected
what is STDP
spike timing dependent plasticity
NMDA receptor
ionotrophic glutamate receptor
Ca2+ channel
DEFINE: habituation
repeated presentation of stimulus leads to a decreased behavioural response
DEFINE: sensitisation
repeated presentation of stimulus leads to an increased behavioural response
why does habituation happen?
- reduced synaptic strength - post-synaptic neuron responds less to stimulus
- reduced neurotransmitter release because readily releasable pool in pre-synaptic neuron depleted
why does sensitisation happen?
- sensory neuron A (senses sensitizing stimulus) synapses onto pre-synaptic terminal of sensory neuron B (senses mild stimulus)
- sensory neuron A releases serotonin
- serotonin binds to g-protein coupled serotonin receptor on pre-synaptic terminal of sensory neuron B
- activates adenylyl cyclase
- adenylyl cyclase converts ATP to cAMP
- cAMP activates PKA
- PKA phosphorylates K+ channel, inactivating it
* results in longer depolarisation so more Ca2+ enters pre-synaptic terminal and causes more vesicular release of neurotransmitters
